Coil and method of making coils



F. E. HENDERSON COIL AND IBTHOD OF MAKING COILS Filed NOV. 14, 1935//vv-ro/? E E HENDERSON ATTORNEY May 31, 1938. I

Patented May 31, 1938 UNITED STATES PATENT OFFICE COIL AND METHOD OFMAKING COILS Application November 14, 1935, Serial No. 49,700

6 Claims.

This invention relates to coils and a method of making coils and moreparticularly to coils having interleaving cellulose acetate sheets.

Investigation has shown that the failure of coils in service is due inmany cases to electrolytic cor rosion caused by moisture gaining accessto ionizable substances in the coil. This permits an electrolyticcurrent to flow due to the difference in potentials in the several partsof the coil. For this reason it has been proposed to hermetically sealcoils to exclude moisture therefrom.

Objects of the present invention are to provide non-corrodible coils anda method of making such coils.

In accordance with one embodiment oi the invention the use of corrosivesubstances in a coil is avoided by winding the coil with enameled wireand interleaving the layers of the coil with cellulose acetate sheets. Amechanical seal is then formed at the ends of the coil by compressingthe ends of the projecting sheets, to prevent the ingress of ionizablesubstances.

A complete understanding of the invention may be had by reference to thefollowing description taken in conjunction with the accompanyingdrawing, in which Fig. 1 is an elevational view partly in sectionshowing a coil embodying the invention;

Fig. 2 is a similar view of a coil with the ends compressed, and

Fig. 3 is a perspective view of the coil shown in Fig. 2.

Referring now more in particular to the drawing, Fig. 1 shows a coilhaving a conductor wound in a plurality of layers 4 of convolutions,each layer being wound upon a sheet of cellulose acetate 5. The outerlayer is also covered with a sheet of cellulose acetate overlapped onthe periphery of the coil and the overlapping portions may be coalescedby the application of a solvent.

Cellulose acetate is free from ionizable substances and in order thatthere will be no ionizable substances in the coil, the conductor isinsulated with a material which contains no ionizable substances. Thisinsulation may comprise a treated silk insulation of a type disclosed inLewis et a1. Patent 1,980,413, November 13, 1934, or it may comprise theusual enamel commonly used for insulating electrical conductors. Sinceall the materials entering the coil are free from ionizable substances,the coil may be exposed to moisture without forming any electrolyteswhich would cause corrosion as the result of electrolytic currentsflowing therein due to the diiference in potential in various parts ofthe coil.

It has been a common practise heretofore to hermetically seal electricalcoils in order to exclude moisture therefrom. This is quite importantwhere the coil contains ionizable substances or in the case where thesurrounding atmosphere is heavily laden with ionizable substances.However, when a coil is made of materials which are free from ionizablesubstances, it is not essential to seal the coils to prevent the ingressof moisture. In many cases even where the atmosphere containssubstantial quantities of ionizable substances it is suflicient to forma mechanical seal not completely impervious at the ends of the coil toprevent the infiltration of such substances into the coil.

In winding a coil in accordance with this invention the ends of thecellulose acetate sheets extend axially beyond the ends of the coils.The ends may then be crushed under a high pressure to firmly compact theprojecting material against the ends of the coil as shown at B in Fig.2. It has been found that a coil will withstand extremely high endpressures and a pressure on the order of 6000 pounds per square inch maybe applied to the ends of the coil without damage to the coil.

This high pressure so thoroughly compacts the projecting ends of thecellulose acetate sheets against the ends of the coil that the compactedends present a smooth, plane surface. The ends thus formed, while theydo not hermetically seal the coil, form a sufficient seal to preventcorrosion of a coil even'in an atmosphere containing substantial amountsof corrosive material.

For use in some locations the coil may be used in the form shown in Fig.1, although in general it is desirable to press the ends of theinterleaving sheets both for the reason above given and also on accountof space requirements.

The coils are preferably wound in multiple on a long mandrel and eachlayer of convolutions of the conductor is wound on a sheet of celluloseacetate having a thickness of less than one mil and as wide as the groupof coils being wound. When the last layer of convolutions has been wounda covering layer 1 of cellulose acetate sheet is applied. After thecoils are removed from the mandrel the cellulose acetate sheets betweenthe coils are cut to separate the coils into individual units. Celluloseacetate sheets of the requislte thinness is available on the market.This material may contain ingredients other than pure cellulose acetateprovided that they consist solely of non-ionizable substances and theterm cellulose acetate" as used in the appended claims is to beunderstood to have tlrls meaning.

It will be understood that the nature and embodiment of the inventionherein describedds merely illustrative, and that many changes andmodifications may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. A coil free from ionizable substances comprising layers ofconvolutions of a conductor insulated with an insulating material freefrom ionizable substances, cellulose acetate sheet material interleavingsaid layers and projecting laterally therefrom, the projecting ends ofthe sheet material being mechanically compacted without mutual adhesionagainst the ends of the coil to form a mechanically crushed butnon-united barrier at the coil ends to close the ends and retard theentry of ionizable substances into the coil.

2. A coil free from ionizable substances comprising layers ofconvolutions of a conductor interleaved with cellulose acetate sheetsextending beyond the ends of the coil, the projecting ends being closelycompacted but not united against the coil ends to form a dense unbondedbarrier for minimizing the entry of ionizable substances at the ends ofthe coil.

3. A coil free from ionizable substances comprising a conductorinsulated with enamel and wound in layers of convolutions, celluloseacetate interleaving sheets between said layers and extending beyond theends of the coil, the projecting ends of said sheets being mechanicallycrushed against the coil ends without being joined to form a denseuncoalesced barrier at the coil ends for retarding the entry ofionizable substances to the coil.

4. A method of making a coil which comprises winding each layer ofconvolutions of a conductor on a sheet of cellulose acetate, said sheetsprojecting beyond the ends of the coil, and mechanically compacting theprojecting portions of the sheets against the coil ends without causingmutual adhesion of the sheets to form a mechanically crushed butnon-united barrier at the coil ends for impeding the entry of ionizablesubstances into the coil.

5. A method ofmaking a coil of non-ionizable materials which compriseswinding each layer of convolutions of a conductor on a sheet ofcellulose acetate, the ends of said sheets projecting beyond the ends ofthe coil, and subjecting the coil to a high endwise pressure tomechanically crush and compact without mutually adhering the projectingportions of the sheets against the coil to form adense uncoalescedbarrier to minimize the entry of ionizable materials into the coil.

6. A method of making a coil which comprises winding each layer ofconvolutions of a conductor on a sheet of cellulose acetate, coveringthe outer layer with a sheet of cellulose acetate, the ends of saidsheets projecting beyond the ends of the coil, and subjecting the endsof the coil to an endwise pressure for the purpose of mechanicallycompacting without coalescing the projecting ends of the sheets toprovide a mechanically crushed but not integrally united barrier at thecoil ends the coil.

FRED E. HENDERSON.

